The present disclosure relates generally to spectral measurement systems and methods. More particularly, the present disclosure relates to a method for enhancing the spectral resolution of a given measurement system such as for example a color measurement system, by using different combinations of illumination sources.
Spectral measurement, for example color measurement, is important for many industries including household consumer products, automobiles, and any number of other examples requiring portability, accuracy and cost-effective solutions. The color in particular of a target object may be characterized by a “spectral reflectance” which can be determined directly via the observed distribution of the proportions of different wavelengths over the extent of the visible range in a continuous spectrum. Unfortunately, many conventional high-resolution spectral measuring devices include or implement complex optical systems that make the product too bulky and expensive for many applications.
Relatively inexpensive and portable spectral measurement devices may be available, but the lower resolution of the associated optical sensors makes these options undesirable at least due to the inaccuracy of spectral data obtained therefrom. When comparing the difference in the way these types of sensors measure color (or comparing the difference in two colors in general), a color difference standard known as ΔE is most typically used. This is a special form of color space “distance” which has been developed to mimic the way the human eye perceives color difference. The process for converting from sense values and minimizing the ΔE between sensor readings and a standard color value is where instrument calibration and setup becomes important, and heavily impacts the accuracy of a color measurement tool.
One known problem with tristimulus sensor based colorimeters is that they lack the specificity of a spectrophotometer due to much fewer independent measurable parameters in the optical spectrum (i.e., an RGB colorimeter might only measure R, G, and B, whereas a spectrophotometer can record high resolution reflectance curves over the visible spectrum). Inherent design differences such as optics, stimulation sources, and detector responses make colorimeters produce a different result from a spectrophotometer and from other colorimeters.
Because of the aforementioned specificity (and greater perceived accuracy), spectrophotometer measurements are often used as reference standard. Interestingly, there does exist variation between any two spectrophotometers, and it is a common practice to calibrate a spectrophotometer to match the readings of a given reference spectrophotometer. The calibrated accuracy of this device will then be based on its conformance to the reference device.
More generally, all color measurement devices are judged based on their conformance to some reference device. Therefore, it would be desirable to provide a system and method capable of allowing less expensive detectors with low spectral resolution to accomplish accurate measurements normally requiring expensive high spectral resolution detectors.